JP2005154277A - Method for converting fluoro carboxylic acids - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method for reducing adverse effects of fluoro carboxylic acids to the environment and living organisms by converting the fluoro carboxylic acids into chemical species with low toxicity and smaller effect to the living organisms. <P>SOLUTION: The method for converting fluoro carboxylic acids comprises decomposition of the fluoro carboxylic acids into fluoro carboxylic acids with less carbon atoms and fluoride ions by irradiating an aqueous solution containing the fluoro carboxylic acids with a light containing UV light in the presence of a gas containing oxygen. At least one kind of fluoro carboxylic acids expressed by formula: C<SB>n</SB>F<SB>2n+1</SB>COOH (in the formula n is an integer of 3-30), are preferred as the fluoro carboxylic acids. The light used in the irradiation preferably comprises UV light containing UV light of ≤350 nm of wave length. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a decomposition and conversion method for converting a fluorocarboxylic acid having an adverse effect on the environment and the human body into a less toxic chemical species and reducing the influence on the environment and a living body.

In recent years, fluorocarboxylic acids such as perfluorooctanoic acid (C ₇ F ₁₅ COOH; abbreviated PFOA), which has been used in the environment as industrial surfactants and raw materials for producing fluoropolymers, are detected. It is becoming an environmental problem (for example, refer nonpatent literature 1). It has been pointed out that these sources are due to thermal deterioration during the production and use of fluoropolymers and during the production and use of fluoropolymers.

Generally, a fluorocarboxylic acid has a strong carbon-fluorine bond and thus exists stably in the environment and remains extremely long.
The accumulation and toxicity of these fluorocarboxylic acids in the living body depend on the number of carbon atoms in the alkyl group of the fluorocarboxylic acid, and the smaller the number of carbon atoms, the lower the impact on the living body (toxicity). For example, trifluoroacetic acid (CF ₃ COOH) having a minimum number of carbon atoms does not accumulate in the human body.
Previously, the present inventors have proposed a method for decomposing a fluorine-based organic compound using a photocatalyst (see, for example, Patent Document 1). However, fluorocarboxylic acids having a small number of carbon atoms in a decomposition reaction of fluorocarboxylic acids. There is no known useful method for reducing the adverse environmental impact by converting to.

Environmental Science and Technology, 37, p312A-313, 2003 Japanese Patent Laid-Open No. 2003-40805

  The present invention has been made in view of the above-mentioned situation in the prior art, and converts fluorocarboxylic acids into chemical species with low toxicity and less influence on the living body, thereby reducing adverse effects on the environment and the living body. The purpose is to provide a simple method.

  As a result of intensive investigations aimed at solving the above-mentioned problems, the present inventors, as a result of irradiating the fluorocarboxylic acid aqueous solution with ultraviolet light under specific conditions, the fluorocarboxylic acid has a higher carbon number along with the generation of fluoride ions. Based on this fact, the present invention has been completed.

That is, the present invention decomposes fluorocarboxylic acids into fluorocarboxylic acids and fluoride ions having fewer carbon atoms by irradiating an aqueous solution containing fluorocarboxylic acids with a light beam containing ultraviolet light in the presence of an oxygen-containing gas. This is a method for converting fluorocarboxylic acids.
The fluorocarboxylic acid is preferably at least one perfluorocarboxylic acid represented by the formula: C _n F _{2n + 1} COOH (where n is an integer of 3 to 30). Moreover, it is preferable that an ultraviolet ray having a wavelength of 350 nm or less is included as a light ray including ultraviolet light to be irradiated.

  According to the present invention, fluorocarboxylic acids that are harmful to the environment and the human body can be efficiently converted into fluorocarboxylic acids with low toxicity and a low number of carbon atoms and fluoride ions by a simple treatment operation.

  In the present invention, since the concentration of fluorocarboxylic acids released into the environment is gradually increasing, and environmental pollution and accumulation and toxicity in living organisms are becoming problems, the fluorocarboxylic acids are easily decomposed and reduced. This is a method for reducing the influence on the environment and living body by converting to fluorocarboxylic acids having a small number of carbon atoms which are toxic chemical species. Fluoride ions produced by this method can be easily captured as calcium fluoride that is harmless to the environment when treated with calcium.

In the present invention, the fluorocarboxylic acid to be converted or decomposed is a compound represented by the formula C _n F _{2n + 1} COOH, and is a perfluorocarboxylic acid having 1 or more, preferably 3 to 30 carbon atoms. Species or two or more kinds, specifically perfluoropropanoic acid, perfluorobutanoic acid, perfluoropentanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid Etc.

In the present invention, an aqueous solution containing these fluorocarboxylic acids is used. The concentration of the fluorocarboxylic acid in the aqueous solution is appropriately determined according to the difficulty of the reaction, but is usually 1 × 10 ^{−6 to} 0.1 mol / L, preferably 10 ⁻⁴ to 10 ⁻² mol / L. . When the concentration is high, the fluorocarboxylic acid may be difficult to dissolve. In such a case, it is preferable to heat to about 40 ° C.
Next, an oxygen-containing gas is introduced into the reaction system of the aqueous solution. When working in air, oxygen is already contained, but oxygen or an oxygen-containing gas containing an inert gas such as air is bubbled into this solution under normal pressure or a reaction to increase the oxygen concentration. The container may be filled with oxygen to about 0.5 MPa. The temperature of the reaction system is preferably about room temperature to 40 ° C.

  The wavelength of the irradiation light may include light of any wavelength as long as it includes an ultraviolet light region of 350 nm or less, which is a wavelength region that can be absorbed by the target fluorocarboxylic acid, and is 200 to 800 nm, preferably 250 to 400 nm. The type of the light source is not particularly limited, and a mercury lamp, a xenon lamp, a mercury xenon lamp, a deuterium lamp, sunlight, or the like may be used as appropriate. Furthermore, the light irradiation time is not particularly limited, and is preferably about 1 hour to 3 days although it depends on the intensity.

Although the mechanism by which the fluorocarboxylic acid is converted into the fluorocarboxylic acid having a smaller number of carbon atoms by the method of the present invention is not clear at present, it is presumed to be due to the following reaction mechanism.
That is, first, when the fluorocarboxylic acid (C _n F _{2n + 1} COOH) as a decomposition raw material is irradiated with light, decarboxylation occurs to generate C _n F _{2n + 1} radicals. This reacts with oxygen to become a C _n F _{2n + 1} OO radical, and further reacts with water to become C _n F _{2n + 1} OOH. Since this substance is unstable, it is immediately pyrolyzed to C _n F _{2n + 1} O, and further reacted with water to C _n F _{2n + 1} OH. Since this alcohol is also unstable, HF is eliminated to form C _n-1 F _2n-1 COF, and finally this hydrolyzes to C _n-1 F _2n-1 COOH (carbon atoms from the starting fluorocarboxylic acid). One less fluorocarboxylic acid).
In this way, the highly toxic fluorocarboxylic acid can be easily converted into a low-toxic fluorocarboxylic acid with reduced carbon and fluorine atoms.

  In order to specifically carry out the reaction of the present invention, for example, the following may be carried out. First, an aqueous solution of fluorocarboxylic acid is placed in the bottom of a reaction vessel capable of light irradiation. Thereafter, in some cases, a gas containing oxygen for increasing the oxygen concentration is introduced. The window material for introducing light attached to the reaction vessel is preferably formed of sapphire because fluoride ions are generated. Next, after irradiating the aqueous solution with light containing ultraviolet rays for a certain period of time, the decomposition products and products in the reaction vessel are recovered.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

22 mL of water in which 2.96 × 10 ⁻⁵ mol of perfluorooctanoic acid (C ₇ F ₁₅ COOH, PFOA) was dissolved was placed in an Inconel reactor (with an internal volume of 154 mL) with a sapphire window and gold-coated inside. Oxygen gas was introduced until the total pressure in the reactor reached 0.48 MPa.
Next, while stirring the solution with a magnetic stirrer, light of 250 to 600 nm was irradiated for 72 hours at 25 ° C. with a mercury xenon lamp. About the product after the completion of the reaction, the remaining unreacted PFOA and the generated fluorocarboxylic acids C ₆ F ₁₃ COOH, C ₅ F ₁₁ COOH, C ₄ F ₉ COOH, C ₃ F ₇ COOH, C ₂ F ₅ COOH and CF ₃ COOH were quantified using ion exclusion chromatography and high performance liquid chromatography in combination, and fluoride ions were quantified by ion chromatography.
The HPLC chromatogram of the solution after the reaction is shown in FIG. In addition, Table 1 shows the quantitative results of the obtained product. As seen in Table 1, the fluorine atom balance (mass balance) before and after the reaction was 96.7%, which was good.

22 mL of water in which 2.95 × 10 ⁻⁵ mol of perfluoroheptanoic acid (C ₆ F ₁₃ COOH, PFHA) was dissolved was placed in an Inconel reactor (with a volume of 154 mL) with a sapphire window and gold-coated inside. The oxygen gas was introduced until the total pressure in the reactor reached 0.49 MPa.
Next, while stirring the solution with a magnetic stirrer, light of 250 to 600 nm was irradiated with a mercury xenon lamp at 25 ° C. for 24 hours to cause a reaction. About the product after the completion of the reaction, the remaining unreacted PFHA and the generated fluorocarboxylic acids C ₅ F ₁₁ COOH, C ₄ F ₉ COOH, C ₃ F ₇ COOH, C ₂ F ₅ COOH and CF ₃ COOH was quantified using ion exclusion chromatography and high performance liquid chromatography in combination, and fluoride ions were further quantified by ion chromatography.
Table 2 shows the quantitative results of the obtained product. As seen in Table 2, the fluorine atom balance (mass balance) before and after the reaction was 99.5%, which was good.

  Since the present invention is a method that can easily reduce the toxicity of fluorocarboxylic acids that adversely affect the environment and living organisms, it is useful for preventing environmental pollution.

It is a HPLC chromatography figure of the reaction solution by the decomposition reaction of the perfluorooctanoic acid obtained by this invention.

Claims (3)

  In the presence of an oxygen-containing gas, an aqueous solution containing fluorocarboxylic acids is irradiated with light containing ultraviolet light to decompose the fluorocarboxylic acids into fluorocarboxylic acids and fluoride ions having fewer carbon atoms. A method for converting fluorocarboxylic acids. Fluoro carboxylic acids, _{formula: C n F 2n + 1 COOH} (. Wherein, is an integer of n = 3 to 30) with at least one perfluoro carboxylic acids is fluoro carboxylic acids of Claim 1 represented Conversion method. The method for converting a fluorocarboxylic acid according to claim 1, wherein the irradiated light including ultraviolet light includes ultraviolet light having a wavelength of 350 nm or less.

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